1. Field of Invention
The invention relates to a common rail fuel injection apparatus and a control method thereof.
2. Description of Related Art
Common rail fuel injection apparatus capable of changing the injection pressure of fuel injected from an injector are known. An example of such common rail fuel injection apparatus is described in Japanese Patent No. 2885076. In the common rail fuel injection apparatus described in Japanese Patent No. 2885076, the injection pressure of fuel injected from an injector is changed by disconnecting/connecting a pressure reduction passage extending between the injector and a return passage through the use of a pressure-increasing piston. More specifically, when the lift of the pressure-increasing piston is less than a predetermined amount, the pressure reduction passage extending between the injector and the return passage is not disconnected by the pressure-increasing piston, but the fuel pressure in the injector is reduced by injection. Conversely, when the lift of the pressure-increasing piston is greater than the predetermined amount, the pressure reduction passage extending between the injector and the return passage is disconnected by the pressure-increasing piston, so that the fuel pressure in the injector is increased.
However, in the common rail fuel injection apparatus described in Japanese Patent No. 2885076, whether the fuel pressure in the injector is to be increased or not is greatly dependent on the relative position of the pressure-increasing piston with respect to the pressure reduction passage. If, for example, the load of a spring that urges the pressure-increasing piston is different from a designed value, there is a possibility that the pressure reduction passage will not be disconnected by the pressure-increasing piston when the pressure reduction passage needs to be disconnected by the pressure increasing piston. There is another possibility that the pressure reduction passage will be disconnected by the pressure-increasing piston when the pressure reduction passage should not be disconnected by the pressure increasing piston. Similar possibilities arise if, for example, the position of the pressure reduction passage is different from the designed position. That is, in the common rail fuel injection apparatus described in Japanese Patent No. 2885076, if factors and the like that determine the relative position of the pressure-increasing piston with respect to the pressure reduction passage are different from the designed factors and the like, there is a possibility that the fuel pressure in the injector is increased when the fuel pressure in the injector should be reduced, or a possibility that the fuel pressure in the injector is reduced when the fuel pressure in the injector should be increased.
Accordingly, it is one aspect of this invention to provide a common rail fuel injection apparatus capable of changing the injection pressure of fuel injected from the injector as requested even if component parts are not processed at such a high precision as needed in the common rail fuel injection apparatus described in Japanese Patent No. 2885076.
This invention provides a common rail fuel injection apparatus capable of changing an injection pressure of a fuel injected from an injector, as described below. That is, the common rail fuel injection apparatus includes a piston for increasing the injection pressure of the injector, a chamber for controlling a position of the piston so as to control the injection pressure, an input constriction that sets an amount of flow of the fuel that enters the chamber, an out put constriction that sets an amount of flow of the fuel that exits from the chamber, and a valve that controls a passage of the fuel from a common rail to the input constriction.
In the common rail fuel injection apparatus, the input constriction is provided to set the amount of flow of fuel that enters the chamber provided for controlling the position of the piston, and the output constriction is provided to set the amount of flow of fuel that exits from the chamber. Furthermore, the input constriction is connected to the common rail via the valve. That is, unlike the case of the pressure-increasing piston described in Japanese Patent No. 2885076, whether the fuel pressure in the injector is increased or not is not greatly dependent on the relative position of the piston with respect to a pressure reducing passage. That is, whether the lift of the piston is reduced is determined in accordance with whether the valve is in the closed valve state. Furthermore, whether the lift of the piston is increased is determined in accordance with whether the valve is in the open valve state. More specifically, if the valve is closed, the amount of flow of fuel that exits from the chamber becomes greater than the amount of flow of fuel that enters the chamber, so that the lift of the piston reduces and the fuel pressure in the injector reduces. Conversely, if the valve is opened, the amount of flow of fuel that exits from the chamber becomes less than the amount of flow of fuel that enters the chamber, so that the lift of the piston increases and the fuel pressure in the injector increases. Therefore, it becomes possible to change the injection pressure of fuel injected from the injector as requested without a need to process component parts with high precision as required for the common rail fuel injection apparatus described in Japanese Patent No. 2885076.
For example, if the valve is formed by a two-way valve, it is possible to change the injection pressure of fuel injected from the injector as requested while employing a simpler construction than the common rail fuel injection apparatus employing a three-way valve as described in Japanese Patent No. 2885076.